1. Field of the Invention
The invention relates generally to a method for producing radioactive isotopes. More specifically, the invention relates to an improved chromatographic extraction method whereby Technetium-99m of high yield and high purity is produced.
2. Background of the Prior Art
Technetium-99m which has a half life of six hours, is produced by the spontaneous radioactive decay of Molybdenum-99, which has a half life of 67 hours. High purity Technetium-99m is used primarly as a radioisotope in medical research and diagnosis. Since the isotope sought to be used has such a short half life, it is common practice to ship the users of Technetium-99m Molybdenum-99. The user then separates the desired amount of Technetium-99m from the Molybdenum-99 as his needs require.
A variety of methods are disclosed in the prior art for separating Technetium-99m from Molybdenum-99. These prior art methods are quite different from the method disclosed herein.
One of these prior art methods, as exemplified by U.S. Pat. No. 3,436,354, is based on liquid-liquid extraction principles, whereby Molybdenum-99 and Technetium-99m are partitioned between two immiscible liquids by constant agitation. This process is non specific and in order to extract high purity Technetium-99m several repeated extractions are necessary; furthermore it allows chemically labile organic solvents to be exposed to strong mineral acids and alkalies, which results in the chemical degradation of the organic phase and contamination of the Technetium-99m.
A second prior art method, as exemplified by U.S. Pat Nos. 3,519,385 and 3,890,244, utilizes principles of precipitation and physical separation of the precipitated Molybdenum-99 from the soluble Technetium-99m by filtration or centrifugation.
A third prior art method as illustrated by U.S. Pat. No. 3,382,152, a paper by J. J. Pinajian "International Journal of Applied Radiation and Isotopes" 17, 664, 1966 and another paper by J. F. Allen "International Journal of Applied Radiation and Isotopes" 16, 334, 1965, each use principles of ion exchange chromatography. In this process an ion exchange column is first preconditioned with an acid solution. Then an acidified solution of Molybdenum-99 is loaded onto the column. The column is again conditioned by using an organic solvent before it is ready for elution with an acidified salt solution or an acidified organic solvent. The shortcomings of this process are (1) the several preconditioning steps that are necessary, (2) the unavailability of usable Technetium-99m on the first day of operation because of radionuclidic Molydenum-99 contamination and chemical alumina contamination, (3) possible degradation of the organic solvent because of acid exposure and (most importantly) (4) because of the relatively low yields of Technetium-99m, e.g., 65-75% yields of Technetium-99m which may be contaminated with radioactive iodine.
The fourth prior art method, as illustrated by U.S. Pat. No. 3,468,808, utilizes chemical reactions between Molybdenum-99 and zirconium oxide, thus allowing Technetium-99m to be eluted from the column using ionic solutions or using an organic solvent.
A further drawback of some of the foregoing methods is that the Technetium-99m is produced in the form of an aqueous solvent whereas production in a solventless, i.e. dry particulate form, would be more desirable for purposes of flexibility in the preparation of diagnostic reagents of desired radioactive concentration. It would be desirable to have a method for producing Technetium-99m in dry, particulate form in high yield and purity, i.e., free from contamination with Molybdenum-99.